1. Field of the Invention
The present invention relates to a process for the viscosification of an aqueous liquid which includes the steps of forming a solvent system of an organic liquid or oil and a polar cosolvent, the polar cosolvent being less than about 15 weight percent of the solvent system, a viscosity of the solvent system being less than about 1,000 cps; forming an interpolymer complex of neutralized sulfonated polymer (water insoluble) and copolymer of styrene/vinylpyridine in the solvent system to form a solution, a concentration of the water insoluble interpolymer complex polymer in the solution being about 0.01 to about 0.5 weight percent, a viscosity of the solution being less than about 200 cps; and admixing or contacting said solution with about 5 to about 500 volume percent water, the water being immiscible with the organic liquid and the polar cosolvent and interpolymer complex transferring from the organic liquid to the water phase, thereby causing the water phase to gel (i.e., thicken). The large increase in viscosity of the aqueous phase is directly attributed to the formation of a large number of minute water-filled particles dispersed in the continuous aqueous phase.
2. Description of the Prior Art
There are many applications for very viscous or gelled solutions of polymers in water which are quite diverse. There are also a number of physical and chemical techniques for preparing such systems. The present invention is concerned with a process for gelling an aqueous system by contacting the aqueous system with a relatively low viscosity, organic liquid solution of an interpolymer complex. The potential applications for this process and the products derived therefrom will be evident in the instant application. Some of these applications are as a viscosifier for aqueous solutions; for viscosification of aqueous acid and inorganic salt solutions; as a fluid loss additive, in enhanced oil recovery; as a viscous foamer in oil well applications; as a water-shut-off means in oil well applications; as a spacer and soluble pig in oil well applications; and as a friction reducer in transferring liquid through a pipe.
The instant invention differs from a number of patents, U.S. Pat. Nos. 4,361,658, 4,322,329 and 4,282,130, filed by Robert D. Lundberg, one of the instant inventors, et al. These previously-filed applications were directed to the gelling of the organic liquid by a water insoluble, neutralized sulfonated polymer, whereas the instant invention is directed to the gelling of an aqueous phase. Quite unexpectedly, it has been discovered that when the concentration of the interpolymer complex in solution is maintained in a critical concentration range of 0.01 to 0.5 weight percent of the total volume of solvent, which is a mixture of non-polar organic liquid and a polar cosolvent, is agitated with an aqueous solution a transfer of the polar solvent and water insoluble interpolymer complex from the organic liquid phase to the water phase occurs. The water insoluble interpolymer complex causes the water phase to gel, wherein the interpolymer complex is insoluble in the water phase. In the previously-filed patent applications substantial viscosification of the non-polar organic liquid phase did not occur until the concentration of the neutralized sulfonated polymer was sufficiently high enough to permit chain entanglement of adjacent polymer molecules, thereby completely filling the solvent space. The gelation of the aqueous phase of the instant invention does not occur by this previously described mechanism because the resultant concentration of water insoluble, interpolymer complex is not sufficiently high enough to permit chain entanglement. The mechanism of gelation of the aqueous phase, as defined in the instant invention, occurs by the formation of macroscopic, spherical polymer membranes or films dispersed throughout the aqueous fluid (i.e., interfacial viscosification) wherein large volumes of the water of the aqueous liquid are encapsulated within a series of minute polymer bags.
The instant invention describes a process which permits (1) the preparation of polymer solution mixture of two or more interacting polymers in organic liquid having reasonably low viscosities (i.e., less than about 200 cps); and (2) the preparation of extremely viscous solutions or gels of an aqueous fluid from such solutions by a process of mixing or contacting water with the polymer solution mixture. These operations are achieved by the use of the appropriate concentration, 0.01 to 0.5 weight percent of water insoluble interpolymer complex, having low concentrations of interacting groups present, preferably metal sulfonate groups and amine-containing groups. The former polymers are described in detail in a number of U.S. patents (U.S. Pat. Nos. 3,836,511, 3,870,841, 3,847,854, 3,642,728 and 3,921,021), which are herein incorporated by reference. These polymers possess unusual solution characteristics, some of which are described in U.S. Pat. No. 3,931,021. Specifically, these polymers, such as lightly sulfonated polystyrene, containing about 2 mole percent sodium sulfonate pendant to the aromatic groups, are typically not soluble in solvents commonly employed for polystyrene itself. However, the incorporation of modest levels of polar cosolvents permit the rapid dissolution of such ionic polymers to form homogeneous solutions of moderate viscosity.
The polymers containing the basic moieties, such as amine groups, are readily soluble in solvents commonly employed for polystyrene itself. In addition, these materials are soluble in solutions containing modest levels of polar cosolvents. More specifically, these polymers, such as styrene-4-vinylpyridine copolymers, contain up to about 15 mole percent 4-vinylpyridine attached to the chain backbone.
In the instant process the role of the polar cosolvent is that of solvating the ionic groups in order to prevent strong association or interaction of the sulfonate groups with the base-containing polymer while the main body of the solvent interacts with the polymer backbone. For example, xylene is an excellent solvent for the polystyrene backbone and when combined with 5% methanol will dissolve, readily and rapidly, the mixture of lightly sulfonated polystyrene and styrene-4-vinylpyridine copolymer to form a relatively low viscosity fluid system. Removal of the polar cosolvent permits interpolymer interactions to occur, resulting in a large viscosity increase.
The remarkable and surprising discovery of the instant invention is that when small (or large) amounts of water are combined and mixed with solutions of interacting polymers dissolved at low concentrations (0.01 to 0.5 weight percent) in such mixed systems as those described above a phase transfer of the water insoluble, interpolymer complex and cosolvent occurs from the non-polar organic liquid phase to the water phase, wherein the water insoluble, interpolymer complex causes the water phase to gel. That is, the aqueous phase is found to contain a large number of minute water-containing particles (normally spheres) dispersed in the continuous aqueous phase. These particles significantly contribute to the marked increase in viscosity. Indeed, it is possible to achieve increases in viscosity of the water phase by factors of 10.sup.3 (1,000) or more by the addition of only 5 to 15% water, based on the polymer solution volume. This unusual behavior is postulated to arise from the removal of the polar cosolvent and water insoluble, interpolymer complex from the organic liquid phase into the separate aqueous phase which then gels, i.e., formation of large numbers of minute, water-filled particles in the continuous aqueous phase.
It should be noted that we have shown (U.S. patent application Ser. Nos. 374,197, 374,198, and 374,251) that sulfonated EPDM and sulfonated polystyrene are very effective as viscosifiers of aqueous systems even though these polymers are soluble only in hydrocarbon solvents (with the aid of a polar cosolvent, such as methanol). We have found that if a dilute hydrocarbon solution (typically 1 g/l or less) containing sulfonated polymer is mixed with water phase separation of the two phases occurs upon standing. Only a small amount of polymer remained in the hydrocarbon solvent, while the majority of the polymer is found in the aqueous phase. Specifically, the aqueous phase contains a large number of small water droplets surrounded by a sulfonated polymer membrane. Unsulfonated polymer produces only a classical phase separation. When the proper volume ratio of hydrocarbon to water is used the aqueous phase becomes completely filled with these spheres. Approximately ten percent of the hydrocarbon solvent is entrapped in the aqueous phase, undoubtedly within the polymer membrane, and also within the sphere itself. Based on previously available information it appears that the sulfonated polystyrene is a more effective viscosifier than sulfonated PEDM, which can be attributed to the higher sulfonation level of the former, as compared to the latter, material.
An important aspect of this instant invention relates to the use of these systems, formed via interpolymer complexes, in aqueous solutions containing large concentrations of acid or salt. The previously described systems, U.S. Ser. Nos. 374,198 and 374,251, using sulfonated polystyrenes, lose their effectiveness in water, but are enhanced in acid-containing water. More specifically, it was found that only the combination of a suitable nonionic surfactant with sulfonated polystyrene gives formulations which are effective in producing these water-in-water pseudo emulsions in high concentrations of salt water. In acidic solutions the nonionic surfactant is not needed for stability (25.degree. C.); however, the viscosity of these systems tends to increase significantly with the addition of small amounts of the nonionic material (typically &lt;0.04 g/l). The system formed with interpolymer complexes has improved stability in both acid and salt solutions; therefore, it is not necessary to utilize a non-ionic surfactant in these instances.
The mechanism through which the family of interpolymer complexes is operative is not totally understood. The preferred species of these materials is lightly sulfonated polystyrene possessing a sulfonated level from approximately 2 mole percent up to at least 6 mole percent, based on present data and amine-containing copolymers, especially styrene-4-vinylpyridine copolymers containing up to moderate levels of base, i.e., .ltoreq.15 mole percent 4-vinylpyridine.
It is readily apparent that sufficient hydrophobic and hydrophilic character has to exist within the molecular structure of these interpolymer complexes for the occurrence of interfacial activity. As a consequence of this "interfacial" activity the interpolymer complexes extremely effective viscosifiers, due essentially to the formation of macroscopic geometrical structures (i.e., spheres). An appropriate term for these structures is water-in-water pseudo-emulsion or water-in-water suspension.